In recent years, for the purpose of reducing environmental load, power generating systems utilizing natural energy, such as solar power generation systems without carbon dioxide emission, are spreading among respective homes. Meanwhile, for dealing with power shortage and the like, development/commercialization is proceeding on a system provided with a storage battery, a system utilizing an electric-powered vehicle as a storage battery, a system combining solar power generation and a storage battery, and the like. In the above systems, a lithium-ion battery is used in many cases as the storage battery.
For example, in Patent Document 1, there is disclosed a configuration and control technique of an insulated-type DC/DC conversion device provided with a storage battery as a secondary battery.
Specifically, in the case of charging the storage battery using power from a DC power source, an AC voltage is generated by a converter in the primary side (in the side where the DC power source is connected), and then the AC power is converted (diode-rectified) to DC power by a converter in the secondary side (in the side where the storage battery is connected) that is connected to the primary-side converter through a transformer. In contrast, in the case of discharging from the storage battery to the DC power source, an AC voltage is generated by the secondary-side converter and the AC power is converted (diode-rectified) to DC power by the primary-side converter.
Meanwhile, according to the power conversion device described in Patent Document 1, in the case of charging to the storage battery, for example, since an AC waveform supplied from the primary side is rectified by the converter connected in the secondary side, it is unable to supply power if a maximum amplitude of the AC waveform supplied to the secondary side is not higher than at least the battery voltage of the storage battery. Likewise, in the case of discharging from the storage battery to thereby supply power to the DC power source in the primary side, since an AC waveform supplied from the secondary side is rectified by the converter connected in the primary side, it is unable to supply power if a maximum amplitude of the AC waveform supplied from the secondary side is not higher than at least the voltage of the DC power source in the primary side.
Thus, in the power conversion device described in Patent Document 1, the turn ratio of the transformer placed between the primary-side and secondary-side converters is changed according to a direction of power supply (charging direction or discharging direction), to thereby control an amplitude of the AC voltage inputted to the converter in the power-supply reception side so as to be higher than the DC output voltage of the converter in the power-supply reception side.